Cell-extracellular matrix (ECM) interactions are key regulators of developmental morphogenic events. Cardiovascular abnormalities associated with the connective tissue disorders Marfan syndrome and congenital contractural arachnodactyly have been linked genetically and biochemically to the microfibrillar ECM proteins fibrillin 1 and 2 respectively. In addition to ocular and skeletal abnormalities, patients with these disorders manifest aortic root dilatation, aortic insufficiency, and mitral valve prolapse. A neonatal form of Marfan syndrome causes severe cardiovascular defects and leads to death within the first year. Epifluorescence microscopy indicates fibrillin-1 and -2 positive fibrils are present in the epicardium, dorsal mesocardium, and enclocardial cushion tissue/valve primordial of avian embryos, and surround the forming bilateral dorsal aortae; implicating the fibrillins in cardiovascular morphogenesis. These microfibrils may impart stability or provide extensible properties to these regions, which are subject to stress/strain. To address the function(s) of fibrillins during early cardiovascular development we will use time-lapse imaging, fibrillin marker antibodies, and computational analyses to document fibrillin assembly/reorganization and motion in the avian embryo bilateral heart forming tissues, endocardial cushions/valve primordia, and major embryonic vessels in normal embryos. Further, we propose to monitor the effects of experimentally perturbing microfibril assembly on cardiovascular development. Similarly, we will monitor the effects of altering cardiovascular (CV) morphogenesis (at the tissue level) on fibrillin assembly. Finally, we will use a complementary mouse explant culture system to monitor dynamically fibrillin assembly in normal and transgenic CV tissue, We hypothesize that dynamic microfibril assembly is key for normal cardiac development, and that disruption of orderly assembly leads to cardiovascular malformations. Examining fibrillin fibril assembly will lead to a better understanding of connective tissue-related cardiovascular defects. [unreadable] [unreadable] [unreadable]